With just a day to go till Apple's much-anticipated launch event, the hype surrounding what the Cupertino-based tech giant could unveil has reached fever pitch.

With rumors suggesting that Apple could be about to show off the new iWatch, investment bank Citigroup has gone to town and detailed what this could mean for the wearables market.

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The release of an iWatch before the coming Holidays sales period could mean 14 million units shifted in 2015 with an expected retail price of $300, according to Oliver Chen, a retail analyst at the bank. For 2016, he expects 20 million units sold.

For revenue this would yield $4.2 billion in 2015 and $6 billion the year after, according to the bank, giving an upside of approximately 2-3 percent of total revenue. It also sees an impact of $0.06-$0.10 on Apple's earnings per share (EPS) in each of these years.

Apple's event begins on Tuesday at 10 a.m. California time and has already led some eager fans to queue up at stores around the globe in anticipation of new product releases. The company is typically tight-lipped on giving away any information, but Reuters reported over the weekend that the company had invited top fashion editors and bloggers to its launch gala, suggesting some sort of a wearable device could be being prepped.

If a smartwatch is launched then, it would mark a key moment for the industry, but wouldn't be the first of its kind to enter the market.

Samsung's Galaxy Gear is noted for being the first major smartwatch to be released and was initially introduced exactly a year ago. Sony, Asus and Motorola are just some of the other brands that have entered a wearables technology market which has been described as "chaotic and immature" by Ben Wood, the chief of research at CCS Insight, who believes it is a space characterized by "significant levels of hype."

Despite the hype, Ciitbank's Chen predicts the market for smartwatches alone will reach $10 billion by 2018 from a figure of around 1.6 billion today. The wider wearables market, which includes sport fitness bands, watches, and apparel could be worth $30 billion by that point, he added. Previous estimates by the International Data Corporation (IDC), said that the global market for wearables will swell to 111.9 million units by 2018 with a growth rate of 78 percent per year.

Meanwhile, analysts at research firm Canalys released a report at the end of August showing that the wearable band market had already grown 684 percent on a worldwide basis in the first half of 2014, compared with the same period last year.

"Most technology companies are waiting to see what Apple will do first. The market will see dramatic change in the coming months and vendors with early-mover advantages will come under pressure," the company said in a press release at the time.